1. Field of the Invention
The present invention provides a milling/sizing apparatus which includes individual and/or nested sieves each of which may also include a quantity of beads, disks and/or other geometric or non-geometric shapes. The sieves can be rotated, vibrated or agitated in any and all combinations by various methods to achieve independently horizontal rotation and vertical reciprocation (similar to a merry-go-round) to efficiently segregate, size or mill cohesive powder particles to specific size ranges. The invention also contemplates use of the apparatus in the sizing and quantification of aggregated particles of cohesive aggregates in general, such as ores, animal and human foodstuffs, fossil fuels, and the like.
2. Statement of the Related Art
Classification of powder particle size, and milling to a specific size range(s) has become of increasing importance in mining, agriculture, energy production, and the like. By way of example there can be mentioned size classification of sulfur, coal, inorganic and organic pigments, grains, starches, sugars, and the like. Attention to particle size is especially critical in the pharmaceutical field (and related fields) due to the increased need to control drug delivery rates. The control of particle size of hydrophobic drug substances has become of major importance in the formulation of solid oral dosage forms (e.g., tablets, capsules), liquids (e.g., suspensions, transdermal), and semisolids (e.g., creams, ointments, lotions, and the like). A substantial need exists for apparatus and method which can separate and/or mill all such materials, and especially cohesive particulate drugs, into the specifically required size ranges better than systems known in the art.
With respect to the present state of the art, Remington's Pharmaceutical Sciences, Easton, Pa., Mack Publishing Company, 18th Edition, page 1617, 1618 and 1620, 1990, notes that commercially available apparatus provide centrifugal impact mills. By means of a rotor, material is milled and pushed through a sieve or screen. As examples, Remington cites the "QUICK SIEVE" (Glatt Air), the "TURBOSIEVE" and the "CO MILL." Also mentioned in Remington are mechanical sifters such as the "GYRO-WHIP" (Sprout-Waldron). It is believed that in none of the foregoing are used multiple sieves with the ability to operate by moving the sieve surface(s) in a horizontally rotating pattern superimposed on a vertically reciprocating pattern and effect segregation milling, i.e., they do not operate like a merry-go-round.
Other prior art apparatus are described in Perry, Chemical Engineers' Handbook, New York, McGraw-Hill Book Company, 5th Ed., pages 21-44 and 21-45, 1973, which illustrates sieves and shakers such as the "RO-TAP" of the W. S. Tyler Company, the "END-SHAK" of Newark Wire Cloth Company, the "DYNAMIC" of SoilTest, Inc., and the "CENCO-MEINSER" of Central Scientific Company. It is believed that in none of the foregoing are used multiple sieves with the ability to operate by moving the sieve surface(s) in a horizontally rotating pattern superimposed on a vertically reciprocating pattern. The use of objects to facilitate the process is not mentioned.
Most of the patent literature related to reciprocating sieve shaker apparatus describes mechanisms for vertically shaking stacks of sieves. Reference is made in this connection to Smith et al, U.S. Pat. No. 3,744,631; Tonjes et al, U.S. Pat. No. 2,959,285; Gundlach, U.S. Pat. No. 4,233,151; Gilson, U.S. Pat. No. 2,358,453. Such devices do not provide for horizontal rotation of the screen stack and they are silent on the possibility of using milling aids to minimize plugging of the sieve openings, reducing agglomerated particles of cohesive substances, and milling powders to any desired size range.
It has now been discovered and is the subject matter of the present invention that if sieves or stacks of sieves are adapted to rotate horizontally and at the same time agitated vertically, cohesive particles are efficiently sized and deagglomerated, especially if the individual sieves are loaded with effective amounts of shaped three-dimensional milling aids.